Process for the manufacture of carbon products



July 28, 1970 LEGENDRE ET AL 3,522,006

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United States Patent 3,522,006 PROCESS FOR THE MANUFACTURE OF CARBON PRODUCTS Andr Legendre, Saint-Cloud, and Henri des Rochettes,

Saint-Jean-de-Maurienne, France, assignors to Pechiney- Compagnie de Produits Chimiques et Electrometallurgrques, Paris, France Filed Nov. 1, 1967, Ser. No. 679,750 Claims priority, application France, Nov. 21, 1966,

rm. or. con) 31/02, 31/04 US. Cl. 23209.3 7 Claims ABSTRACT OF THE DISCLOSURE The invention is addressed to the manufacture of amorphous or graphitized carbon products from crude carbonaceous products in an electrical furnace of the Acheson type in which use is made of a granulated carbonaceous material surrounding the crude products and in which the improvement comprises the utilization of panels of an electrically insulating substance positioned between the products and the source of electrical current in a direction perpendicular to the direction of current to reduce the passage of electrical current through said products, at least during passage of the products through a critical heating range.

This invention is addressed to the manufacture of carbon products in an electrical furnace of the Acheson type.

The invention relates to the treatment of crude products shaped of a mixture of carbonaceous base material such as coke and a carbonaceous binder such as pitch.

Heretofore, such crude products have been treated by heating in a combustion furnace, such as a tunnel furnace, or a chamber furnace, heated by producers gas or mazout gas wherein the crude products are raised to a temperature of about 600 to 120-0 C. Such treated products, referred to as burned products, can be marketed with the carbon in the form referred to as amorphous carbon. The amorphous carbon of the burned products can be converted to graphite by subsequent heat treatment in an electrical graphitization furnace.

Such electrical graphitization furnaces are of the type conceived by E. G. Acheson in 1895 in which the product to be graphitized is located between two current supply heads with the space between the products being filled with granulated carbonaceous material, generally re ferred to as the granulated charging material, and which completely surrounds the products. The granulated charging material is formed partially of new coke, i.e. which has not previously been employed in the assembly of an Acheson furnace, and'partially of granulated material recovered from a previous graphitization operation. The resistor ,is usually brought up to a temperature of 2700 to 2900 C.

Crude products have also been charged directly into an electrical graphitization furnace without previous heat treatment for burning. In such instance, the burning and graphitization are carried out as a single operation, without intermediate cooling. Such single step process provides a number of advantages, such as savings in time, heat, labor and materials, and lower original investment costs.

Unfortunately, elements produced by such single step process have frequently been found to have poor texture, fissures or cracks, particularly with elongate or solid elements of large diameter, such as 250 mm., with the result that the percentage of rejects is relatively high.

As rejects, reference is made to shaped products that are commercially unacceptable by reason of imperfect texture, fissures or cracks developed during treatment in the Acheson type furnace.

It is believed that such deficiencies are caused primarily by imbalance in temperature distribution in the transverse section of the resistor during burning but no means have been found to the present to overcome these deficiencies in an eflFective and efiicient manner.

It is an object of this invention to provide a method and means for overcoming the described deficiencies of present practice and it is a related object to provide a method and means which makes use of an electrical furnace of the Acheson type for the manufacture of burned or graphitized carbon products from crude products.

These and other objects and advantages of this invention will hereinafter appear and for purposes of illustration, but not of limitation, an embodiment of the invention is shown in the accompanying drawings in which- FIG. 1 is a sectional view of an Acheson furnace resistor with panels embodying the features of this invention;

FIG. 2 is a sectional view taken along the line A-B of FIG. 1; and

FIG. 3 is a sectional view taken lengthwise in a vertical plan along the line C-D.

In accordance with the practice of this invention, the crude products are burned in an electrical furnace of the Acheson type comprising a carbonaceous granulated charging material which surrounds the crude product, characterized by interposition, in the passage of the electrical current between the crude products, of panels of an electrically insulating substance oriented perpendicularly to the direction of the current and then preferably subjecting the burned product to graphitization without intermediate cooling, thereby to achieve burning and graphitization in a single operation.

The investigations have established that the temperature imbalance is produced chiefly in a critical temperature zone, generally in the range of 250 to 650 C., and that it is due to a particularly sharp drop in resistivity of the crude products during the temperature rise of the furnace. When certain portions of the resistor reach the temperature within the critical range, while adjacent portions have not yet reached such temperature, the resistivity of the portions overheated decreases rapidly whereby the density of the current passing through the overheated portions increases proportionately. Once initiated, such imbalance continues to increase during the rise in temperature.

It is the concept of applicants to interpose electrically insulating panels into the path of the electrical current to the effect that the passage of electrical current through the product is greatly reduced to completely suppressed and so that the temperature distribution in the transverse section of the resistor of the furnace is made substantially uniform, notwithstanding the disturbing influence of the rapid decrease in resistivity of the products during the rise in temperature.

For this purpose, use can be made of panels of various electrically insulating materials such as asbestos and asbestos cement.

In accordance with a preferred practice of this invention, the electrically insulating panels are formed of a carbonaceous material such as wood fibers bonded with a phenol aldehyde resin, corrugated cardboard or the like materials which can be reduced to a carbonaceous residue after burning. By such arrangements, the passage of electrical current through the product is greatly reduced to completely suppressed during all or a major part of the time that the products are in the above defined critical temperature range. In accordance with the practice of the invention, the passage is substantially reestablished as the panels undergo carbonization during the progressive heating of the furnace and the carbonization is practically completed by the time that the products have reached a temperature exceeding the critical range.

The thickness of the panels may be varied over a fairly wide range such as from 2 mm. to cm., depending somewhat upon the nature of the electrically insulating substance of which the panels are formed. The surface area of the panels is selected to be within the range of 0.4 to 2 times and preferably 0.8 to 1.2 times the transverse section of the crude products in the resistor.

It is also desirable to extend the panels in the granulated charging material to a level below the upper level of the crude products in the furnace.

In one modification, the panels are positioned with their upper ends below the upper ends of the crude products so that current is free to pass between the upper end portions of the products. Under such circumstances, the upper portion of the resistor, which has a tendency to heat up more slowly than the remainder, will be heated additionally by the passage of said current.

It is possible, by the practice of this invention, to obtain graphitized products having mechanical and thermal shock characteristics higher than products manufactured of the same materials in the current manner. This advantage is particularly evident when the elements to be graphitized are large and elongated or solid form having a diameter or cross-section that exceeds 250 mm. The concepts of this invention find beneficial use in the preparation of large electrodes used in steel works where it is desirable to have electrodes characterized by high mechanical strength and resistance to thermal shock.

It is possible, in accordance with the practice of this invention, to carry out the burning operation separate and apart from and without being followed by graphitization thereby to produce an amorphous carbon product of excellent texture and With very little rejects. Such procedure may also be followed when it is desired to effect an impregnation of the burned products before graphitization.

Referring now to the drawings for a description of the invention, 1 indicates the crude products to be graphitized; 2 represents the granulated charging material arranged in accordance with the practice of this invention; 3 is the panels, and 4 represents the heat insulating material surrounding the resistor. The arrows indicate how the passage of electrical current is greatly reduced or even entirely suppressed through the products by reason of the presence of the electrically insulating panels.

The following Examples 1 and 2, represented in the tabulation, are both concerned with the burning and graphitization of crude products in an Acheson furnace in a single operation. In Example 1 the single operation is effected in accordance with the prior art while Example 2 makes use of the process and concepts of this invention. In each of the two examples, the furnace charge is formed of 36 tons of crude products of cylin- Example 1 Example 2 according to according to the prior art the invention Temperature of the upper part of the shaped elements when their lower part reaches 850 C Peroent of rejeets It will be understood that changes may be made in the details of construction and arrangement of the panels and in the formulation thereof without departing from the spirit of the invention, especially as defined in the following claims.

We claim:

1. In the process for the manufacture of amorphous or graphitized carbon products from crude carbonaceous products by heating in an electrical Acheson type furnace having granulated carbonaceous material surrounding the crude products, the improvement comprising positioning panels of electrically insulating material between said products and the source of electrical current in a direction perpendicular to the direction of current to reduce the passage of electrical current through said products.

2. The process as claimed in claim 1 in which the passage of electrical current through said products is eliminated in the areas blocked by said panels.

3. The process as claimed in claim 1 in which both burning and graphitization are carried out in a single operation.

4. The process as claimed in claim 1 in which the panels are formed of a carbonizable material.

5. The process as claimed in claim 1 in which the resistance to the passage of electrical current is substantially eliminated by the time that the carbonaceous products reach completion of the reaction temperature.

6. The process as claimed in claim 1 in which the panels are positioned to extend below the lower ends of the crude products.

7. The process as claimed in claim 1 in which the panels are positioned with their upper ends below the upper ends of the crude products.

References Cited STATES PATENTS EDWARD J. MEROS, Primary Examiner US. Cl. X.R. 13-7 

